U.S. patent application number 12/077182 was filed with the patent office on 2008-09-25 for headlight control device.
This patent application is currently assigned to DENSO CORPORATION. Invention is credited to Kenji Kobayashi, Yukimasa Tamatsu.
Application Number | 20080231195 12/077182 |
Document ID | / |
Family ID | 39773999 |
Filed Date | 2008-09-25 |
United States Patent
Application |
20080231195 |
Kind Code |
A1 |
Kobayashi; Kenji ; et
al. |
September 25, 2008 |
Headlight control device
Abstract
In a vehicle headlight apparatus, a projection unit having a
same structure of an LED projector receives a light provided from a
lamp. The projection unit generates and projects a projection image
toward a vehicle front-area. A vehicle ECU has an image signal
obtaining means for obtaining image signals representing a vehicle
front-area image, a high brightness area determination means for
analyzing the image signals in order to successively determine a
high brightness area in the image signals, and a projection image
determination means for determining a projection image so that the
light, corresponding to the high brightness area and to be
irradiated toward the vehicle front-area, becomes weak when
compared with the light previously determined. Thereby, an
intensity of the light to be irradiated to an object with a high
reflection factor can be decreased. This can suppress decreasing of
driver's frontal visibility.
Inventors: |
Kobayashi; Kenji; (Nagoya,
JP) ; Tamatsu; Yukimasa; (Okazaki-shi, JP) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Assignee: |
DENSO CORPORATION
Kariya-city
JP
|
Family ID: |
39773999 |
Appl. No.: |
12/077182 |
Filed: |
March 17, 2008 |
Current U.S.
Class: |
315/82 |
Current CPC
Class: |
B60Q 1/085 20130101;
B60Q 1/143 20130101; B60Q 2300/45 20130101 |
Class at
Publication: |
315/82 |
International
Class: |
B60Q 1/08 20060101
B60Q001/08 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 19, 2007 |
JP |
2007-071212 |
Claims
1. A headlight control device for a vehicle headlight apparatus
comprising a light source and a projection unit, in which the
projection unit receives the light provided from the light source,
and generates a projection image using the received light and
projects the image toward a front area of a vehicle, the headlight
control device comprising: image signal obtaining means that
successively obtains image signals representing a front area image
of a vehicle provided from a vehicle-mounted camera when a
projection image is projected toward a front area of the vehicle;
high brightness area determination means that analyses the image
signals obtained by the image signal obtaining means, and
successively determines a high brightness area in the image
signals; and projection image determination means that determines a
projection image to be transmitted to and generated in the
projection unit so that the light, corresponding to the high
brightness area in the image signals determined by the high
brightness area determination means, to be irradiated toward a
front area of the vehicle becomes weak when compared with the light
which is previously determined.
2. The headlight control device according to claim 1, wherein the
projection image determination means determines the high brightness
range in the projection image which corresponds to the light
brightness area in the image signals, and then determines a bright
range in the projection image so that the bright range does not
include the high brightness range in the projection image.
3. The headlight control device according to claim 2, wherein the
projection image determination means determines the projection
image so that an upper limit of the bright range is lower than a
lower limit of the high brightness range in the projection
image.
4. The headlight control device according to claim 2, wherein the
projection image determination means determines the projection
image so that the bright range becomes a range obtained by
eliminating the high brightness range in the projection image from
the bright range in the previous projection image which is obtained
immediately before.
5. The headlight control device according to claim 2, wherein the
projection image determination means determines the high brightness
range in the projection image which corresponds to the light
brightness area in the image signals, and then determines a color
of the high brightness range in the projection image so that the
color becomes a low brightness color when compared with that of the
previous projection image.
6. The headlight control device according to claim 5, wherein the
projection image determination means determines the brightness of
the color of the high brightness range in the projection image so
that the brightness of the high brightness area determined by the
high brightness area determination means becomes lower than a
reference brightness which is determined in advance.
7. A method of controlling a projection image to be projected by a
vehicle headlight apparatus comprised of a light source and a
projection unit, wherein the projection unit receives a light
provided from the light source and generates a projection image
using the light and projects the projection image toward a front
area of a vehicle, the method of comprising steps of: successively
obtaining image signals which represents a front area image of the
vehicle provided from a vehicle-mounted camera when an projection
image is projected toward the front area of the vehicle; analyzing
the image signals, and successively determines a high brightness
area in the image signals; and determines a projection image so
that the light, corresponding to the high brightness area in the
image signals and to be irradiated toward the front area of the
vehicle, becomes weak when compared with the light which has been
previously determined, and transmitting the projection image to the
projection unit.
8. The method of controlling a projection image according to claim
7, wherein the high brightness range in the projection image which
corresponds to the light brightness area in the image signals is
determined, and then a bright range in the projection image is
determined so that the bright range does not include the high
brightness range in the projection image.
9. The method of controlling a projection image according to claim
8, wherein the projection image is determined so that an upper
limit of the bright range is lower than a lower limit of the high
brightness range in the projection image.
10. The method of controlling a projection image according to claim
8, wherein the projection image is determined so that the bright
range becomes a range obtained by eliminating the high brightness
range in the projection image from the bright range in the previous
projection image which is obtained immediately before.
11. The method of controlling a projection image according to claim
8, wherein the high brightness range in the projection image which
corresponds to the light brightness area in the image signals is
determined, and a color of the high brightness range in the
projection image is determined so that the color becomes a low
brightness color when compared with that of the previous projection
image.
12. The method of controlling a projection image according to claim
11, the brightness of the color of the high brightness range in the
projection image is determined so that the brightness of the high
brightness area becomes lower than a reference brightness which is
determined in advance.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is related to and claims priority from
Japanese Patent Application No. 2007-71212 filed on Mar. 19, 2007,
the contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a headlight control device
to be installed in a vehicle headlight apparatus utilizing a
projector device for motor vehicles.
[0004] 2. Description of the Related Art
[0005] There is known a vehicle headlight apparatus that utilizes a
projector device. For example, Japanese patent laid open
publication No. JP 2004-136838 has disclosed such a vehicle
headlight apparatus utilizing a transmission type liquid crystal
projector device. In the vehicle headlight apparatus, a light
source irradiates a light into a liquid crystal panel. The light is
then projected to a front area of a vehicle through one or more
lenses.
[0006] In the vehicle headlight apparatus disclosed in JP
2004-136838, a predetermined optical image is formed in the liquid
crystal panel in order to control a propagation direction and a
range of a high beam light and a low beam light as well as a color
of the light.
[0007] In the related-art technique disclosed in JP 2004-136838,
when a car navigation system makes information regarding a current
vehicle position and a vehicle moving direction, the vehicle
headlight apparatus displays such information on a road. The
vehicle headlight apparatus further displays other information, for
example, an arrow mark on a road, which indicates the direction of
left-turn when a driver instructs the left-turn to the vehicle.
[0008] By the way, when a headlight apparatus irradiates a high
beam light onto a distant area on the road, the driver's frontal
visibility generally increases. However, there is a possibility of
there being things with a high reflection factor on the road in a
front area of the moving vehicle, such as signboards, traffic
signs, preceding vehicles, oncoming vehicles, or pedestrians with
reflection tape. Those things often reflect light irradiated from
headlight lamps of the vehicle toward the direction of the vehicle
driver. This situation decreases the driver's frontal
visibility.
[0009] In the related-art techniques, the driver switches to the
low beam light from the high beam light when the driver's frontal
visibility decreases.
[0010] Although there is a similar possibility of the drivers
frontal visibility decreasing when the headlight apparatus
irradiates a high beam light, the vehicle headlight apparatus
utilizing a projector device has an advantage in that it can change
a headlight irradiation range and a headlight color.
SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to provide a
headlight control device, that utilizes a feature of a projector
type vehicle headlight apparatus, capable of suppressing any
decrease of a driver's frontal visibility even if a high reflection
object is present in a front area of a vehicle.
[0012] To achieve the above purposes, the present invention
provides a headlight control device to be installed to a vehicle
headlight apparatus. Such a vehicle headlight apparatus is
comprised of a light source and a projection unit which receives a
light provided from the light source and generates a projection
image using the received light and projects the image toward a
front area of a vehicle.
[0013] In particular, the headlight control device has an image
signal obtaining means, a high brightness area determination means,
and a projection image determination means. The image signal
obtaining means successively obtains image signals which represent
a front area image of a vehicle provided from a vehicle-mounted
camera when a projection image is projected toward a front area of
the vehicle. The high brightness area determination means analyses
the image signals obtained by the image signal obtaining means, and
successively determines a high brightness area in the image
signals. The projection image determination means determines a
projection image to be transmitted to and generated in the
projection unit.
[0014] The image signal can be broken into information concerning
brightness levels, and this is determined by the light brightness
area determination means. The strength of the light to be
irradiated toward the front area of the vehicle can then be made to
be weaker, taking into account the areas of high brightness in the
image signals, resulting in a weaker light.
[0015] According to the present invention, the front area image of
the vehicle is analyzed in order to determine the high brightness
area in the image signals. Further, the projection image is
determined so that the light to be irradiated to the front area of
the vehicle corresponding to the high brightness area becomes weak.
Accordingly, even if a vehicle driver is temporarily dazzling
reflections of the light from an object of a high reflection factor
such as a traffic sign, the intensity of the light to be irradiated
to the object is decreased by determining the area including the
object as the high brightness area. Because this can decrease the
intensity of the reflected light from the object, it is possible to
suppress any lessening of the driver's frontal visibility.
[0016] There is another approach in decreasing the intensity of
light to be irradiated to the front area of the vehicle
corresponding to the high brightness area. That is, in the vehicle
control device, as another aspect of the present invention, the
projection image determination means determines the high brightness
range in the projection image which corresponds to the light
brightness area in the image signals, and then determines a range
of brightness in the projection image so that the brightness range
does not include the high brightness range in the projection
image.
[0017] The present invention provides another following
modification. The projection image determination means determines
the projection image so that an upper limit of the bright range is
lower than a lower limit of the high brightness range in the
projection image.
[0018] The present invention also provides another following
modification. The projection image determination means determines
the projection image so that the bright range becomes a range
obtained by eliminating and replacing the high brightness range in
the projected image with the brightness range taken from the
previously taken image signals.
[0019] The former modification can decrease calculation load
because the upper limit of the range of brightness in the
projection image is only switched to the lower limit. On the
contrary, in the latter modification, it is possible to keep the
driver's frontal visibility because a high beam light can be
maintained.
[0020] The present invention provides another approach to decrease
the intensity of light corresponding to the high brightness area,
to be irradiated to the front area of the vehicle. That is, in the
headlight control device as another aspect of the present
invention, the projection image determination means determines the
high brightness range in the projection image which corresponds to
the light brightness area in the image signals, and then determines
a color of the high brightness range in the projection image so
that the color becomes a low brightness color when compared with
that of the previous projection image.
[0021] In this approach, because the vehicle headlight apparatus
irradiates the light to the object of a high reflection factor
which is present in a front area of the vehicle corresponding to
the high brightness area so that the driver is not dazzling
reflections of the light from the object, it is possible to enhance
the driver's frontal visibility to the object.
[0022] When the color light is switched, it is preferable that the
projection image determination means determines the brightness of
the color of the high brightness range in the projection image so
that the brightness of the high brightness area determined by the
high brightness area determination means becomes lower than a
reference brightness which is determined in advance. This can
decrease the intensity of the reflection light, reflected from the
object which is present in the front area of the vehicle,
corresponding to the high brightness area, to a low intensity, so
that the driver is not dazzling reflections of the light from the
object.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] A preferred, non-limiting embodiment of the present
invention will be described by way of example with reference to the
accompanying drawings, in which:
[0024] FIG. 1 shows a schematic configuration of a vehicle
headlight apparatus equipped with a headlight ECU according to an
embodiment of the present invention;
[0025] FIG. 2 shows an example of a front image of a vehicle
represented by image signals obtained by the headlight ECU shown in
FIG. 1, and in particular, shows a high brightness area in the
image; and
[0026] FIG. 3 is a flow chart showing a method of controlling a
projection image by the headlight ECU according to the present
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] Hereinafter, various embodiments of the present invention
will be described with reference to the accompanying drawings. In
the following description of the various embodiments, like
reference characters or numerals designate like or equivalent
component parts throughout the several diagrams.
First Embodiment
[0028] A description will be given of a headlight electric control
unit 2 (hereinafter, referred to as the "headlight ECU 2" for
short) as a headlight control device according to a first
embodiment of the present invention with reference to FIG. 1, FIG.
2, and FIG. 3. The headlight ECU 2 as the headlight control device
according to the present invention is installed to a vehicle
headlight apparatus 1.
[0029] FIG. 1 shows a schematic configuration of the vehicle
headlight apparatus 1 equipped with the headlight ECU 2 according
to the first embodiment of the present invention.
[0030] As shown in FIG. 1, the vehicle headlight apparatus 1 is
comprised of a lamp 3 as a light source, a projection unit 4, and
the headlight ECU 2. Although FIG. 1 shows only the lamp 3 and the
projection unit 4, an actual vehicle is equipped with a pair of the
lamps 3 (a right headlamp and a left headlamp) and a pair of the
projection units 4 (as a right projection unit and a left
projection unit). A pair of the lamps 3 and a pair of the
projection units are disposed at a front end part of a vehicle.
[0031] In the embodiment, well-known various types of lamps such as
a halogen lamp and a xenon lamp are available as the lamp 3. The
headlight ECU 2 performs On/Off control of the lamp 3.
[0032] The projection unit 4 in the vehicle headlight apparatus 1
has a same structure of a projection unit in an available
transmission type liquid crystal projector. That is, the projection
unit 4 is comprised of a primary dichroic mirror 41, a secondary
dichroic mirror 42, a first mirror 43, a second mirror 44, a third
mirror 45, a red color liquid crystal panel 46R, a green color
liquid crystal panel 46G, a blue color liquid crystal panel 46B, a
prism 47, and a projection lens 48.
[0033] The primary dichroic mirror 41 is capable of selectively
reflecting green light and blue light, and on the contrary, capable
of transmits red color.
[0034] On the other hand, the secondary dichroic mirror 42 is
capable of selectively reflecting green light and capable of
transmits red light and blue light. The primary dichroic mirror 41
and the secondary dichroic mirror 42 are disposed in the projection
unit 4 so that the secondary dichroic mirror 42 faces a reflection
surface of the primary dichroic mirror 41.
[0035] Green light and blue light reflected by the primary dichroic
mirror 41 come to the secondary dichroic mirror 42.
[0036] The secondary dichroic mirror 42 transmits blue light and
reflects green light toward the prism 47.
[0037] The first mirror 43 completely reflects toward the prism 47
light (namely, red light) transmitted through the primary dichroic
mirror 41.
[0038] The second mirror 44 completely reflects toward the third
mirror 45 light (namely, blue light) transmitted through the
secondary dichroic mirror 42.
[0039] The third mirror 45 completely reflects light transmitted
from the second mirror 44 toward the prism 47.
[0040] The red color liquid crystal panel 46R generates various
types of images (optical images) under the control of the headlight
ECU 2. The red color liquid crystal panel 46R is disposed between
the first mirror 43 and the prism 47. Red color light provided from
the first mirror 43 transmits through the red color liquid crystal
panel 46R, and a red color image thereby enters into the prism
47.
[0041] The green color liquid crystal panel 46G also generates
various types of images (optical images) under the control of the
headlight ECU 2. The green color liquid crystal panel 46G is
disposed between the secondary dichroic mirror 42 and the prism 47.
Green color light provided from the secondary dichroic mirror 42
transmits through the green color liquid crystal panel 46G, and a
green color image thereby enters into the prism 47.
[0042] The blue color liquid crystal panel 46B generates various
types of images (optical images) under the control of the headlight
ECU 2. The blue color liquid crystal panel 46B is disposed between
the third mirror 45 and the prism 47. Blue color light provided
from the third mirror 45 transmits through the blue color liquid
crystal panel 46B, and a blue color image thereby enters into the
prism 47.
[0043] The prism 47 receives the red color image provided from the
red color liquid crystal panel 46R, the green color image provided
from the green color liquid crystal panel 46G, and the blue color
image provided from the blue color liquid crystal panel 46B, and
then synthesizes those images to generate a projection image. The
prism 47 then projects the projection image toward the projection
lens 48.
[0044] When each of the liquid crystal panels 46R, 46G, and 46B
provides no image, the projection image becomes a white color image
that represents only an outline determined by each of the liquid
crystal panels 46R, 46G, and 46B.
[0045] The projection lens 48 magnifies the light provided from the
prism 47, and projects the magnified light toward the front area of
a vehicle. As a result, the projection image synthesized by the
prism 47 is magnified and the magnified projection image is
projected toward the front area of a vehicle.
[0046] In the embodiment, a size and shape of the projection lens
48 is determined so that the irradiation range of a projection
image to be projected toward the front area of a vehicle can cover
all of an irradiation range on a high beam light and an irradiation
range on a low beam light.
[0047] The headlight ECU 2 is a computer system equipped with a
central processing unit (CPU), a read only memory (ROM), a random
access memory (RAM), and the like. The headlight ECU 2 executes
programs using a temporary memory in the RAM. Those programs are
stored in advance in the ROM. That is, the headlight ECU 2 serves
as an image signal obtaining means 21, a high brightness area
determination means 22, and a projection image determination means
23.
[0048] FIG. 3 is a flow chart showing a method of controlling a
projection image by means of the headlight ECU 2 according to the
present invention. In the vehicle headlight apparatus 1, the
headlight ECU 2 generates the projection image and transmits the
generated one to the projection unit 4. The projection unit 4
irradiates a light based on the projection image transmitted from
the headlight ECU 2.
[0049] The image signal obtaining means 21 obtains image signals
provided from a vehicle-mounted camera 5 every predetermined period
of time when the projection unit 4 projects a projection image
toward the vehicle front area (step S301).
[0050] The vehicle-mounted camera 5 is capable of scanning an image
of the vehicle front area. A position and a scanning range of the
vehicle-mounted camera 5 are set in advance in order to photograph
the entire of the projection image regardless of a size and a range
of the projection image. For example, the vehicle-mounted camera 5
is disposed at a vehicle compartment ceiling.
[0051] The high brightness area determination means 22 receives the
image signals transferred from the image signal obtaining means 21,
and then analyses the image signals, and successively determines a
high brightness area in the image signals (step S302). For example,
there is a following analyzing method of determining the high
brightness area in the image signals.
[0052] A brightness value of each pixel in the image signals
corresponding to the vehicle front area is determined. Binary
processing is carried out in order to obtain the brightness value
of each pixel in the image signals based on a reference brightness
value that has been determined in advance. According to a
well-known labeling method, the area, whose brightness value is not
less than a reference brightness value, is extracted.
[0053] Instead of using such a labeling method, it is also possible
to judge that a brightness value of each pixel is within a high
brightness area or not.
[0054] FIG. 2 shows an example of the vehicle front-area image
represented by image signals obtained by the headlight ECU 1 shown
in FIG. 1. In particular, FIG. 2 shows a traffic sign 8 as the high
brightness area in the image.
[0055] In the case shown in FIG. 2, the headlight ECU 2 according
to the present invention determines the traffic sign 8 as the high
brightness area. It is also possible that the headlight ECU 2
receives detection signals provided from an obstacle sensor 6 (see
FIG. 1), and estimates a relative distance between the obstacle and
the vehicle, and then limits a range for the image analyzing to a
part of the vehicle front-area image based on the estimation result
before initiating the image analyzing by the headlight ECU 2. A
millimeter band radar sensor and a laser radar sensor are available
as the obstacle sensor 6.
[0056] The projection image determination means 23 successively
determines a projection image which will be projected by the
projection unit 4 so that a light is not irradiated to the area in
the vehicle front area, corresponding to the high brightness area
determined by the high brightness area determination means 22 (step
S303). The projection image determination means 23 then controls
the operation of the red color image provided from the red color
liquid crystal panel 46R, the green color image provided from the
red color liquid crystal panel 46G, and the blue color image
provided from the red color liquid crystal panel 46B in the
projection unit 4 in order to correctly generate the determined
projection image (step S303).
[0057] In case of the example shown in FIG. 2, the projection image
determination means 23 successively determines the projection image
so that the light is not irradiated to the traffic sign 8.
[0058] In order not to irradiate the light to the traffic sign 8,
the range in the projection image corresponding to the traffic sign
8 (namely, the high brightness area in the vehicle front-area
image) is eliminated from a bright range. In the embodiments of the
present invention, the bright range is defined as the range in the
projection image that is generated by the light provided from the
lamp 3 as the light source, and then transmits through at least one
of the red color liquid crystal panel 46R, the green color image
provided from the red color liquid crystal panel 46G, and the blue
color image provided from the red color liquid crystal panel 46B in
the projection unit 4.
[0059] Although the high brightness range in the projection image
is determined within a range corresponding to the high brightness
area in the vehicle front-area image, it is possible to determine a
wider range so long as it includes the range corresponding to the
high brightness area.
[0060] There is another preferred modification to eliminate the
high brightness range from the bright range in the projection
image, in which an upper limit of the bright range in the
projection image is changed to a lower side rather than the bottom
limit of the high brightness range in the projection image. In this
case, as shown in FIG. 2, the upper limit of the irradiation range
of the light is switched from the line H1 to the line H2. That is,
the upper limit of the bright range is switched.
[0061] Further, there is another preferred modification to
determine the range of brightness by subtracting the high
brightness range in the projection image from a range of brightness
in a previous projection image before determining the traffic sign
8 as the high brightness area. In case of this modification,
because a high beam light of the vehicle can be continued, it is
possible to keep the driver's frontal visibility. However, because
a relative position between a surrounding object and the vehicle
are successively changed when the vehicle moves, the high
brightness range in the projection image is also changed.
Accordingly, in case of this modification, there is a need to
successively determine the high brightness range in the projection
image.
[0062] In order to satisfy this demand, the projection image can be
successively analyzed. Instead, it is also possible to calculate a
difference of the relative position between the surrounding object
and the vehicle based on the current position of the vehicle that
is successively detected by a position detector 7, and to change
the high brightness range in the projection image based on the
change of the calculated relative position.
[0063] As described above, according to the first embodiment of the
present invention, the high brightness area is successively
determined by analyzing the image of the vehicle front area
provided from the vehicle-mounted camera 5, and the projection
image is determined so that the light is not irradiated to a part
in the vehicle front area corresponding to the high brightness
area.
[0064] As a result, even if the vehicle driver is temporarily
dazzling reflections of the light from the object of a high
reflection factor such as the traffic sign 8 shown in FIG. 2,
because the headlight ECU 2 in the headlight apparatus 1 determines
the area including the object with the high reflection factor as
the high brightness area, and provides the light of low brightness
to the object with a high reflection factor, the intensity of the
reflection light from the object with a high reflection factor
becomes weak. This can suppress the decrease of the driver's
frontal visibility
Second Embodiment
[0065] A description will be given of the vehicle headlight
apparatus 1 equipped with the headlight ECU 2 according to a second
embodiment of the present invention.
[0066] The second embodiment according to the present invention
will explain a modification 23-1 of the projection image
determination means in the headlight ECU 2 in the vehicle headlight
apparatus 1. Because other components of the second embodiment are
the same as those in the first embodiment, the explanation of the
same components is omitted here.
[0067] The projection image determination means 23-1 decreases the
brightness of the high brightness area to a value of not more than
a reference brightness value by changing to a dark color in the
range of the high brightness range in the projection image.
[0068] Specifically, like the first embodiment, the high brightness
area determination means 22 receives image signals provided from
the image signal obtaining means 21, and then determines the range
of a high brightness range in a projection image corresponding to a
high brightness area in the image signals of the vehicle front
area.
[0069] In the second embodiment, it is possible to determine a wide
range for the high brightness range in the projection image so long
as it includes the range corresponding to the high brightness area
in the image signals of the vehicle front area. For example, it is
acceptable to determine the range that covers all areas whose
coordinates are the same in vertical direction of those of the high
brightness range. This case determines a belt shaped range in the
projection image.
[0070] Next, the projection image determination means 23-1
determines a more dark color in the high brightness range in the
projection image when compared with a color in a previous
projection image.
[0071] It is possible to use a predetermined dark color whose
brightness is determined in advance, or possible to decrease the
brightness of such a dark color according to a difference between
the brightness value in the high brightness area in the image
signals of the vehicle front area and a reference brightness
value.
[0072] In the former case, there is a possibility of not adequately
decreasing the brightness of the image in the vehicle front area by
changing once the color of the high brightness range in the
projection image. In this case, a color in the high brightness
range in the projection image is changed several times.
[0073] When the color in the high brightness range in the
projection image is changed to a more dark-brightness color, the
light transmitting through the high brightness range in the
projection image becomes weak. As a result, the vehicle headlight
apparatus 1 can irradiate the light to an object in the vehicle
front area, corresponding to the high brightness area so that the
vehicle driver is not dazzling reflections of the light from the
object. This can suppress decrease of the driver's frontal
visibility. Because headlights also irradiate the light to such an
object in front of the vehicle, the driver's frontal visibility to
the object also increases.
[0074] The present invention is not limited by the first and second
embodiments. It is possible to apply the concept of the present
invention to various applications within the scope of the present
invention. For example, although the projection unit 4 has a same
structure of a transmission type liquid crystal projector, it is
possible that the projection unit 4 in the vehicle headlight
apparatus has a same structure of another type of projectors such
as a DLP (digital light processing) projector and a CRT
projector.
[0075] While specific embodiments of the present invention have
been described in detail, it will be appreciated by those skilled
in the art that various modifications and alternatives to those
details could be developed in light of the overall teachings of the
disclosure. Accordingly, the particular arrangements disclosed are
meant to be illustrative only and not limited to the scope of the
present invention which is to be given the full breadth of the
following claims and all equivalent thereof.
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